It’s not unusual for people in mid- to late life to rerun the “what ifs” of their youth. Many people start reconnecting with people who knew them when they were young. Part of it is simple curiosity. Partly it is an effort to feel young again by revisiting our youth. Part of it is sometimes competitive. Usually it is harmless. Sometimes it leads to reconnecting with people who remember us when . . . and who can again become important friends.
What is unusual and worrisome about your husband’s behavior is that he is hiding his activity and seems to be confining his searches to old girlfriends. You stated that your marriage hasn’t always been good. At 50+, your husband may be feeling that if he is to have the option to make a change, it’s now or never.
You are right to be concerned. You are going to get nowhere by being “wildly jealous” and accusatory. You are not going to help the situation by turning into a sleuth. Your efforts only make the other women look even better to him.
If your marriage is to make it through this crisis, you two need to finally confront the issues that have made things less than good and see whether you can reclaim and rekindle the love and respect you have had.
I suggest you take the high road and apologize for your own out-of-control behavior. Tell your husband that you love him and want your marriage to continue, that you feel threatened by his interest in other women, and that you don’t want to abandon a lifetime together that has been mostly good. Make an appointment with a couples therapist. Ask your husband to go with you. Even if he won’t go, go yourself. A therapist may help you identify ways to more effectively work on your marriage so that your husband will eventually want to join in the project.
I’m sure this is a scary time for you. Please limit contact with anyone who badmouths your husband or who sees all men as impossible. You need people around you who understand what you see in your husband and who give you love and support as you try to turn things around.
I wish you well.